The basic elements of a typical air conditioning unit 1 are a compressor 2, condenser 3, thermal expansion valve 4 and evaporator 5. A schematic diagram of a typical existing system is shown in FIG. 1. The equipment is typically laid out such that the evaporator is inside the air handling ductwork of the building to be cooled in order to provide cooling of the recirculated inside air 6. The compressor and condenser are typically located outside the building to reject the heat to the outside air 7. Interconnecting piping joins the internal portion of equipment to the external.
Normal controls provided with the unit work in a cycle based on temperature demand called by a thermostat. Refrigerant is expanded through a thermal expansion valve which lowers the pressure and temperature of the refrigerant. The refrigerant, now cold, passes through the evaporator coil which is located within the inside air duct. Hot indoor air forced past the evaporator is cooled and provided to the air distribution network. The refrigerant fluid absorbs heat during this step and returns to the compressor for a repeat of the cycle. Refrigerant is compressed in the vapor form as it passes through the compressor and routed through the condenser which rejects heat to the outside air and condenses most of the refrigerant to a liquid.
It is very important in the operation of such a system that the refrigerant entering the compressor is in a vapor state as liquid cannot be compressed. If refrigerant returns to the compressor containing a portion of liquid, a condition called liquid slugging, damage will occur to the compressor.